Air Conditioning

[rjfvillarosa]

I am looking for some help with the air-con on my wifes car, I know that the systems are basically the same on all cars so i am looking for specific help with a 2001 Pontiac Sunfire.
About twelve months ago I noticed a reduction in the amount of condensation falling on the floor of the carport after my wife came home from work. At first I just put it down to the time of year and the climate, but after a while it started to bother me until one day on a long journey the air-con stopped blowing cold air after about an hour into the journey.
After moving the airflow direction control about for a while the air-con came back on and during subsequent trips this procedure always cleared the problem for awhile but it didn't take long to happen again.
I asked around a few people I know and they all said the drain tube from the evaporator is blocked and you need to clean it out. Because this problem doesn't occur on short journeys it has taken a back seat in my list of jobs to do on the car.
About six months ago the blower stopped working on speeds one and two, I checked on rockauto.com and in my manual and found that the car is fitted with an inline resistor that controls the speed, it was only fifteen bucks and a doddle to fit, BUT, in researching the resistor I noticed that you can buy the whole heater/air-con control assembly and that the airflow direction control is vacuum operated (whats that all about? and its $200 for a new one).
My son was here on a visit a few weeks back and we were disscussing the problem with the air-con when he mentioned that in the UK you can buy a cleaning spray that you spray into the heater/air vents whilst the air-con is on full blast and it clears any mould or mildew build up in the evaporator and we noticed on one journey that there was a very feint odour coming through the vents. During my last trip to San Juan the air-con cut out as usual after about an hour and this time instead of my wife switching the airflow control through all the different positions I had her set it in one position and turn off the air-con, my theory being that the evaporator is getting blocked with ice and not allowing air through.

I know this is a little long winded but if there is anyone who is familiar with this specific car/system I wanted them to know all the facts.

The outlet/drain tube from the evaporator is not a long pipe hanging down the bulkhead its just a small 90 degree elbow, so cleaning that out like I was told is a non-starter.

How does the vacuum system for the air direction control work? and if it's not working could it affect the production of cold air?

Does my idea that the evaporator could be gunked up after all these years and that it is not clearing the condensation which is then in turn freezing and restricting the flow of air sound feasible?

Is it possible to remove or access the evaporator for cleaning without discharging the system?

I have tried to buy the cleaning spray my son talked about but I cant find it here on the island anywhere.

The system is fully charged with gas and the compressor cycles on and off exactly as it should.

I used this site and some of their products to make sure the gas was ok and the compressor was working correctly:
http://www.id-usa.com/how_to.asp

Any help on this would be greatfull appreciated.

[glc]

If the evaporator is icing up, you most likely are either overcharged or undercharged. Another possibility is problems with the low and high pressure cutout switches. I don't think problems with the blend door would cause those symptoms, but a bad controller module might.

[thefultonhow]

If the air is still blowing, even if it's not cold, the mode door is fine, so you can ignore that. The low and high pressure switches may be combined in a "dual pressure switch" -- at least, that's how it is on my G20.

[MaxRat]

could be many problems on that car... the module that turns of the water flow to the heater core could also be losing its signal and letting water flow into the heater core and the AC is trying to cool warm air...

if the Cold air is cycling then it can be either the vacuum doors, heater core water valve or the limit switch on the Evap can.... can you hear the AC compressor cycle at all...?

it will cycle while idle but should run constant at road speeds... if it gets too low it will cut out until low side pressure comes back up from the high side bleed-off....

best thing it to check the pressure on the low side with a gauge at 2500rpm...and reference check...

[rjfvillarosa]

Originally Posted by glc Another possibility is problems with the low and high pressure cutout switches.

Any idea how I can test for this?

Originally Posted by thefultonhow If the air is still blowing, even if it's not cold, the mode door is fine, so you can ignore that.

There is a noticeable difference in the amount of air pressure when the cold air stops blowing and as soon as the air gets cold again the pressure returns.

Originally Posted by MaxRat best thing it to check the pressure on the low side with a gauge at 2500rpm...and reference check...

As soon as I have five minutes peace and quiet I will try that one.

Thanks guys.

[glc]

If that were an old R-12 system, I could probably figure out what's going on with a set of gauges and a duct thermometer. However, I have never even touched a R-134 system. I assume the principles are the same, but the "standard" pressures may differ.

With R-12, this was expected behavior - with the system on, the low side should run at ~ 30, the high side at ~ 160. The electric engine fan should be running constantly with the A/C on. Running the engine at ~ 2000 rpm, the low side will slowly drop, and the compressor should cut off before the low side drops to 20. The pressures should go toward equalization, then the compressor should come back on. If the high side goes over 200, either you are overcharged or there's a blockage in the refrigerant system or there is insufficient airflow through the condenser. If it gets really too high, the fusible plug in the accumulator will blow out. Sticking a thermometer in a dash vent should give you ~ 40 degrees, but it will rise if you drop back to idle. The hotter it is outside, the higher the high side pressure will be, and if it's much over 80 degrees outside, the dash temp may not get down to 40.

If the low side pressure drops below 30 and stays there, the evaporator will freeze up. This is usually a faulty low pressure cutout switch. The lower the low side pressure, the colder the air will be.

A trained tech can observe gauge behavior and tell if it's overcharged or undercharged.

The system is fully charged with gas and the compressor cycles on and off exactly as it should.

Exactly how have you determined this? You may want to bite the bullet and take it in and get it properly serviced - which is leak test the system, evacuate it, and recharge it exactly by weight.

If you think the evaporator fins are clogged with crap, you *should* be able to get at it without cracking any fittings - it's either under the dash or in a doghouse on the firewall, probably not too far from the heater core. A repair manual should tell you where and how.

[MaxRat]

Glc...

with R134 it's exactly the same but the low side pressure is lower...25psi is normal and 15psi is the cutoff limit...

high side will be about the same....

if the system is fully charged it should not cycle at 2500rpm....maybe once in a great while...

while I have gauges and I do check temps I fill the AC with R134a while the engine is at 2500rpm and just fill it to the point that the AC compressor doesnt cycle....

if the dryer and screens are clean this usually results me with nice 35f degree temps out of the vents...

Another thing to check as well RJ...is to clean the condenser in front of the radiator...if you travel in dusty conditions the dust gets on the condenser making it unable to transfer heat as effectively as it should...I use a good heavy degreaser and keep it wet and let it soak about 15minutes and then hose it off clean....that will also help with cooling issues

[rjfvillarosa]

Originally Posted by glc Exactly how have you determined this?

By following the videos that I downloaded from the site I linked to in the first post, I am sure I followed what they said but I certainly bow to superior knowledge.
I have a major busy week again next week including a three hundred mile return drive to San Juan in the morning and 'yes' I am taking the Pontiac.
Thanks for all the help so far gentlemen I do appreciate it and G. I haven't ruled out the idea of putting it in somewhere to be diagnosed, there are two good air-con shops within spitting distance of here.
Tomorrow on the way to and from San Juan I will try and note some of the symptoms more closely and let you know and hopefully next weekend I can try a few of your suggestions.
Thanks again guys.

[rjfvillarosa]

On the way to SJ yesterday the air-con faded out after about an hour, the air pressure/volume from the face level vents fell away to practically nothing, you could just about feel cold air blowing from the vents.
I turned the airflow control from recirc to fresh-face level / floor and made sure the air-con was switched off, after about twenty minutes I switched it back to recirc which automatically switches the air-con back on and it was blowing quite strong and very cold.

Any ideas?

[glc]

The evaporator is freezing up. Get a thermometer to stick in the dash outlet and that should confirm it - if the air temp drops much below 40 it's gonna freeze up. Why is it freezing? Incorrect charge level or a low pressure switch that's faulty and not kicking the compressor off.

Try driving it in the normal A/C mode (fresh air) instead of recirc - does it do the same thing?

[rjfvillarosa]

Originally Posted by glc Try driving it in the normal A/C mode (fresh air) instead of recirc - does it do the same thing?

The next long journey that will allow me to check that is in about two weeks, in the mean time I will see what I can find out about the low pressure switch.
Thanks G.

[MaxRat]

if you can find a low side gauge cheap pick it up...find the specs on the low side limit switch and reference that with the gauge...

the switch should shut the compressor off if the low side pressure falls under spec...

if it cycles alot it needs a little freon..if it doesnt then the switch maybe bad...

[jessho]

The low side guage on a manifold has a pressure gauge and corrsponding markings below for the ambient temperature for that pressure for the different freons the guage is designed for. Otherwise, the correct pressure for the freon, when the system isn't running, should match the ambient temperature for that pressure, for that freon. If the temperature for that pressure doesn't match the ambient temperature, then the charge is wrong, which is most situations means there isn't enough freon. The lower pressure will indicate that the ambient temperature should be lower than it actually is. Low pressure will cause the evaporator to freeze intially. Eventually there will be no cooling at all, which usually is found when the low pressure switch on the dryer shuts the compressor down.

It the pressure is low, you have a leak, which will continue to leak until it's found and fixed. If not, and the evaporator coil in the dash is freezing, you're not getting enough air flow through the coils. I've seen this happen when critters get into the plenum and build nests, and I've seen it happen when the cabin filter gets really dirty, or the coil gets full of gunk from years of use.

I've never worked on a sunfire, but more than likely, it's not nearly as bad to get to the evaporator coil than most people think. If you're mechanically inclined, have a service book and a Saturday free, you can get to the coil and at least see if it's clogged, or there's a problem with a direction door. If there's a cabin filter, you should be able to get to it in a short period of time and change it without hardly any trouble.